Polythiophenes have been studied extensively due to their interesting electrical and/or optical properties. Polythiophenes become electrically conducting upon chemical or electrochemical oxidation or reduction. Their ultimately achievable electrical conductivity is determined by their chemical composition, the stereoregularity of the polymerization of the thiophene monomers in the polythiophene chain and by their π-conjugation lengths. Such stereoregularity problems do not arise when unsubstituted thiophenes or thiophenes substituted in the 3- and 4-positions with identical groups are polymerized.
EP-A 257 573 discloses an intrinsically electrically conductive polymer, wherein through connection in the 2-position and/or the 5-position are coupled to one another, statistically averaged from 60 to 100% by weight structural units, which are derived from at least one monomer of the formula (1):
in which R1 is a C1–C2-alkoxy group or —O(CH2CH2O)nCH3 with n=1 to 4 and R2 is a hydrogen atom, a C1–C12-alkyl group, a C1–C12-alkoxy group or —O(CH2CH2O)nCH3 with n=1 to 4, or R1 and R2 together are —O(CH2)m—CH2— or —O(CH2)m—O— with m=1 to 12, 0 to 40% by weight structural units, which are derived from at least one monomer of the formula (2):
wherein R4 and R5 are independently of one another a hydrogen atom, a halogen atom, a C1–C12 alkyl group or aryl or together with C-atoms connected to them form an aromatic ring, R3 and R6 independently of one another represent a hydrogen atom or R3 together with R4 and the C-atoms connected to them or R5 together with R6 and the C-atoms connected to them each form an aromatic ring, X represents an oxygen atom, a sulfur atom, a ═NH group, a ═N-alkyl group or a ═N-aryl group, 0 to 40& by weight structural units, which are derived from at least one monomer of formula (3):
where R7, R8, R9 and R10 independently of one another represent a hydrogen atom, a C1–C12 alkyl group, a C1–C12 alkoxy group or an aryl group, Y and Z independently of one another represent an oxygen atom, a sulfur atom, a ═NH group, a ═N-alkyl group or a ═N-aryl group, R11 represents an arylene group, a heteroarylene group or a conjugated system of the formula (CH═CH)o, wherein o is 1, 2 or 3, 0 to 40& by weight structural units, which are derived from at least one monomer of formula (4):
wherein R12 and R13 independently of one another represent a hydrogen atom, a halogen atom, a C1–C12 alkyl group, a C1–C12 alkoxy group, a C1–C4 alkylamino group or a C1–C4 acylamino group, R14 represents a halogen atom, a C1–C12 alkyl group, a C1–C12 alkoxy group, a C1–C4 alkylamino group or a C1–C4 acylamino group and X has the meaning given above, wherein the polymer in the oxidized form is completely soluble in dipolar aprotic solvents at 25° C. and solutions with a content of at least 0.1 g of the polymer in 100 mL solvent at 25° C. are obtained.
EP-A 339 340 discloses a polythiophene containing structural units of the formula:
in which A denotes an optionally substituted C1–C4-alkylene radical, its preparation by oxidative polymerization of the corresponding thiophene and exemplifies poly(3,4-ethylene-dioxythiophene), poly[3,4-(1′-methyl)ethylenedioxy-thiophene], poly[3,4-(1′-n-hexyl)-ethylene-dioxythiophene) and poly[3,4-(1′-n-decyl)ethylenedioxythiophene]. B Sankaran and J. R. Reynolds in 1995 in Polymer Material Science and Engineering, volume 72, pages 319–320 disclosed the synthesis of 3,4-(1′-n-octyl)ethylenedioxy-thiophene, 3,4-(1′-n-tetradecyl)-ethylenedioxythiophene and their corresponding homopolymers and D. M. Welsh et al. in 1997 in Polymer Preprints, volume 38(2), page 320 disclosed acrylate- and glyme-substituted 3,4-(1′-hydroxymethyl)-ethylenedioxythiophene). S. C. Ng et al. in 1997 in Journal of Materials Science Letters, volume 16, pages 809–811 disclosed the synthesis of 3,4-(1′-allyloxymethyl)ethylenedioxythiophene, 3,4-(1′-glycidoxymethyl-ethylene)dioxy-thiophene and 3,4-(1′-ω-hydroxyhexyloxymethyl)-ethylenedioxythiophene, 3,4-(2′-allyloxymethyl-propylene)dioxy-thiophene, 3,4-(2′-glycidoxy-methyl)propylenedioxy-thiophene and 3,4-(2′-ω-hydroxyhexyloxy-methyl)propylenedioxy-thiophene and their corresponding homopolymers. O. Stephan, et al. in 1998 in Journal of Electoanalytical Chemistry, volume 443, pages 217–226 disclosed the synthesis of 3,4-(1′-ω-sulfobutyloxymethyl)ethylenedioxythiophene and the corresponding homopolymer. P. Scottland et al. in 1998 in J. Chim. Phys., volume 95, pages 1258–1261 disclosed the synthesis of 3,4-(1′-n-hexyloxymethyl)-ethylenedioxythiophene, 3,4-(1′-n-octyloxymethyl)ethylenedioxy-thiophene, 3,4-(1′-n-decyloxymethyl)ethylenedioxythiophene, 3,4-(1′-n-dodecyloxymethyl)ethylenedioxythiophene, 3,4-(1′-n-tetradecyloxymethyl)ethylenedioxythiophene, 3,4-(1′-n-hexadecyloxymethyl)ethylenedioxythiophene and their corresponding homopolymers. S. Akoudad et al. in 2000 in Electochemistry Communications, volume 2, pages 72–76 disclosed the synthesis of 3,4-(1′-(polyoxyethyleneoxymethyl-ethylene)dioxy-thiophene and the corresponding homopolymer.
D. M. Welsh et al. in 1999 in Polymer Preprints, volume 40(2), page 1206 disclosed the synthesis of 3,4-(2′,2′-dimethyl)-propylenedioxythiophene and 3,4-(2′,2′-diethyl)propylenedioxythiophene by a transetherification reaction and polymers derived therefrom. L. J. Kloeppner et al. in 1999 in Polymer Preprints, volume 40(2), page 792 also disclosed the synthesis of 3,4-(2′,2′-diethyl)propylenedioxythiophene, 3,4-(2′,2′-dibutyl)propylene-dioxythiophene and 3,4-(2′,2′-dioctyl)propylenedioxythiophene by a transetherification reaction and polymers derived therefrom.
M. Lemaire et al. in 1988 in Journal of the Chemical Society Chemical Communications page 658 disclosed the polymerization of the chiral thiophenes: (S)(+)- and (R)(−)-2-phenylbutyl ether of 3-propylthiophene. M. M. Bouman et al. in 1995 disclosed the polymerization of poly{3-[2-((S)-2-methylbutoxy)ethyl]thiophene}. Furthermore, G. Bidam, S. Guillerez and V. Sorokin in 1996 in Advanced Materials, volume 8, pages 157–160 disclosed the preparation of regioregular poly[3-(S-3′,7′-dimethyloctyl)-thiophene]. They showed that if the steric group is far enough removed from the backbone then the conjugation is relatively unaffected and this polymer exhibited large conformational changes induced by minute solvent variation.
B. Groenendaal, G. Zotti and F. Jonas in 2001 in Synthetic Metals, volume 118(1–3), pages 105–109 disclosed the conductivity of electrochemically polymerized 3,4-(1′-methyl)ethylenedioxy-thiophene, 3,4-(1′-n-hexyl-ethylene)-dioxythiophene, 3,4-(1′-n-decyl)ethylene-dioxythiophene and 3,4-(1′-n-tetradecyl)ethylene-dioxythiophene and established that poly(3,4-ethylenedioxy-thiophene)s substituted at the 1′-position with n-alkyl groups with 10 carbon atoms or less exhibited lower electrical conductivities than that of poly(3,4-ethylenedioxythiophene). Poly(3,4-ethylenedioxythiophene) substituted with a n-C14H29 group exhibited a 30% increase in electrical conductivity compared with poly(3,4-ethylenedioxy-thiophene) from 650 to 850 S/cm.
A general drawback of conductive polymers which have been prepared and studied up to now, is that their conductivities are still too low for certain applications, their visible light transmittances are insufficiently high and/or they are not processable.